default basic theme for fastapi-simple-auth

How to create/use custom theme:

1. fork this repo to create your theme
2. change content and pyproject.toml
3. install your package in virtualenv with your app and fastapi-simple-auth with pip3 install git+https://github.com/NAME/PACKAGE) or install with pip3 install -e PATH as editable.
4. set your theme name in .env file as TEMPLATE_THEME=your_theme_package_name